In the other game, resident GM Ben Finegold played the Philidor defense and drew by repetition on move 29 against young GM Ray Robson. Finegold said his 17. Qg4 and 18. Qg6 was home preparation.

Nakamura said he tried to surprise his opponent with an offbeat variation in response to the Ukrainian’s Berlin defense against the Ruy Lopez.

“I decided to try the idea of Nd2, Nb3,” Nakamura said in post-game commentary with International Master John Donaldson and Woman Grandmaster Jen Shahade. “I completely underestimated all the counterplay he gets. It was all very unpleasant to say the least.”

Nakamura said his 24th move, Qh3, was ugly, “but the only way to hold the game.” Ponomariov traded queens, giving his opponent doubled h pawns.

“The computer says black is better, but it’s hard for us humans to play these positions,” Nakamura said. “When you’re playing someone strong like Ruslan is, you can’t make dubious moves in the opening like I did.”

Ponomariov, a former world champion, leads the 10-game match 1.5 to .5.

Finegold said he may have played Philidor’s defense “maybe 20 years ago” and saw Robson had played against it only two times.

“He’s pretty good at openings,” Finegold said.

Finegold played the modern order of moves with 1.d6. On move four, Robson could have brought about a trade of queens, forcing Finegold to recapture with the king on d8, losing the right to castle.

“I thought about it a little,” Robson said after the game, “but I’ve not looked at that line; Black seems to do OK. Some recommend it for white. I haven’t looked at it.”

Finegold said the opening “looked like an open Sicilian where both players played weird.”

Robson said that at the end of the game he wanted to place his bishop on d3, but Finegold’s knight on c5 prevented it.

After Finegold originally placed his knight on the c5 post on move 12, he said Robson had to play 13. NxNf6.

Live commentary by IM John Donaldson and WGM Jennifer Shahade can be found at livestream.com/uschess. Rounds and commentary are open to club members, and memberships start at just $5/month for students or $12/month for adults.